The present invention relates to the application of coatings and, more specifically, to an apparatus and method for spray coating the interior surfaces of manholes, wetwells and, generally, the surfaces of structures which are often symmetrical.
In recent years, the general public has become greatly concerned over the ecological condition of the environment. This concern has, in large part, been focused on water pollution and the contamination of the potable water supply by such detrimental agents as raw sewage, chemical waste and the like. For example, procedures for the transportation and disposal of raw sewage and other environmental pollutants have become significantly more rigorous due to environmental legislation and regulations.
Likewise, the condition of drinking water has been of concern. Seepage of toxins, emanating from the ground and from other sources of toxic waste, can contaminate potable water supplies.
Conduit seepage often provides the greatest challenge to rendering the transport of both waste and potable water environmentally sound. Conduits used to transport sewage and potable water are often fabricated of semi-porous materials such as concrete, cement aggregate or terra cotta. Environmentally damaging waste will often seep out of porous conduits into the surrounding soil so as to contaminate surrounding groundwater resources. Conversely, toxins can seep into potable water conduits contaminating water flowing through the conduit.
Coatings applied to the interior surfaces of these conduits can greatly aid in the reduction of seepage. These coatings, which must themselves be environmentally safe, are very often applied to the interiors of the conduits by spraying the coating liberally about the interior surface in order to effectively seal the interior of the conduit.
In large cities, sewer and potable water systems often consist of vast mazes of interconnected subterranean conduits accessed at intervals by manholes or wetwells which lead down to the conduit interiors. Because seepage may also occur through the interior surfaces of manholes and wetwells, the manhole surfaces must also be coated with a coating substance designed to seal the manhole and minimize seepage of toxic substances into the surrounding environment.
The effective application of coatings to the vertical surfaces of manholes, wetwells or other vertical shafts or conduits has proven to be particularly difficult. Typically, a spray gun operator is lowered by rope or cable into the manhole to be coated. Most conventional spray coating application systems require that a human operator be physically adjacent to the area to be coated. Suspended by rope, the spray gun operator applies the coating to the surface of the manhole using a spray gun or nozzle apparatus.
This system is extremely undesirable due both to the dangers inherent to the person applying the coating and to the often haphazard results achieved by the applying the coating in this manner. Obviously, because the spray gun operator is dangling at the end of a rope, a substantial risk of injury exists. Moreover, the presence of the spray gun operator in an enclosed area containing a substantial amount of airborne atomized spray coating, which can be hazardous when inhaled over prolonged periods, poses another very significant health risk to the spray gun operator. In the same vein, manholes and wetwell shafts may often contain toxic gases and contaminants which, after prolonged exposure, can adversely effect the health of the spray gun operator.
Additionally, as the spray gun operator is raised up the manhole, his dangling legs, feet, arms or equipment may strike the surface which has just been coated, thereby undermining the integrity of the newly applied coating and causing a thinly coated or uncoated area where seepage will likely occur. Thus, the presence of a spray gun operator in the manhole or other vertical shaft for the purpose of applying coatings is extremely undesirable.
The material used to coat vertical surfaces, such as manholes and other vertical shafts, typically consists of a polymer formed in situ from two components: a liquid resin base and a curing catalyst. The liquid resin base is designed to cure and harden into a solid resin shortly after the curing catalyst is added to it so that it will not run down the vertical surface being coated. The resin base and curing catalyst should ideally be mixed immediately prior to applying it to the surface to be coated.
Consequently, a number of spray apparatus have been designed to apply the curing coating immediately after the resin base and the curing catalyst have been mixed. The most popular coating application apparatus, as noted, is the spray gun. These spray guns might typically include two atomizer nozzles: one for atomizing the liquid resin base and the other for atomizing the curing catalyst. The two nozzles are disposed such that the dispersion paths of the liquid resin base and the curing catalyst cross and, ideally, the two components intermix prior to application to the surface to be coated. Another type of spray gun system has only one nozzle having an antechamber where the two components are mixed.
However, spray guns are not particularly well adapted for use in vertical environments. As noted, the spray gun operator must be located adjacent to the surface to be coated. Consequently, the spray gun operator must be lowered into the manhole. Because manholes and wetwells are frequently lined with a cement and gravel aggregate mixture, the spray gun operator must take great care to apply the coating liberally at various angles of spray incidence. If the spray gun operator fails to apply the coating from various angles of incidence, discontinuities and rough and uneven areas along the surface may not be completely coated.
Hence, a need exists in the art for a method and apparatus for thoroughly applying multicomponent coatings to the enclosed vertical surfaces of manholes or access conduits without the necessity of lowering a spray gun operator into the manhole or conduit.